1. Field of the Invention
The present invention relates to a system for producing a pulse signal for controlling an internal combustion engine, including a digital control means such as a microcomputer. More specifically, the invention relates to a system which is capable of maintaining the engine operation in case of a failure or a malfunction of an arithemetic unit of the digital control means.
2. Description of the Prior Art
With the recent advancement of microcomputer technology in the field of automobile electronics, digital control means have been developed for controlling the fuel supply amount or the ignition timing of an internal combustion engine.
Digital control means of the above stated type have the advantages of performing accurate and stable control over a long term.
However, once an arithmetic unit of the microcomputer fails to work properly, the unit has a fatal effect on the engine operation; in other words, it becomes completely impossible to maintain the engine operation and a vehicle provided with such an engine is rendered uncontrollable, because it is very likely that the digital arithmetic unit ceases to produce an output signal or it produces an erroneous or random output.
On the other hand, although a system having an analog control means generally suffers from drift it still is capable of maintaining engine operation and thus is advantageous in that the vehicle provided with such a system is still operable in case of a malfunction therein.
However, this type of control means has many defects, such as lack of stability during the long term operation, which requires very fine adjustment for maintaining accurate control, and causes low productivity.